Personalised nutrition in Elderly
Obesity rates are rising among older adults and this is associated with increased risk for diseases like diabetes and heart disease, reduced physical function and increased disability risk. Fat mass loss in obese older adults has many beneficial effects including a reduction in disease risk and improved quality of life. However, the recommendation of weight loss in obese older adults remains somewhat controversial, due to concerns that calorie restricted diets designed to reduce excess fat mass may simultaneously ‘accelerate’ the age-related loss of muscle mass and function (termed sarcopenia) and further exacerbate disability risk. Therefore, we urgently require strategies to help obese older adults lose fat while preserving important muscle mass.
Our recent study shows that performing resistance exercise (i.e. lifting weights) while on a weight loss diet boosts rates of muscle building and therefore may help obese older adults to lose fat while preserving important muscle.
This study set out to improve our understanding of how diet and physical activity can be manipulated to minimise muscle mass loss during weight loss in overweight and obese older adults.
On a traditional weight loss diet around 25% of the weight we lose is lean mass – a major component of which is muscle. This is a particularly problematic for older adults as this may accelerate the detrimental loss of muscle that occurs with age. Previous research shows that weight loss diets suppress the rate of muscle protein synthesis (muscle building) which may explain why we lose muscle as well as fat mass.
We investigated whether performing resistance exercise training during weight loss could counteract the negative effect of a reduced calorie diet on muscle protein synthesis. We were also interested in finding out whether the spread of dietary protein (found in foods like dairy, fish, meat and beans) over the day had an impact on the rate of muscle protein synthesis during weight loss. Most people eat protein in a skewed pattern - eating small amounts of protein at breakfast and lunch and a large serving of protein at dinner. However, a moderate serving of protein (approximately 30 g of protein per meal) has previously been shown to maximally stimulate muscle protein synthesis in the hours following the meal in older adults. Therefore, we thought that a more even spread of protein over the daily meals, with a moderate serving of protein at each meal, may result in higher rates of muscle protein synthesis compared to a traditional, skewed pattern.
Significance
What is novel / significant about this finding? We found that the overall rate of muscle protein synthesis was 26% greater when older men performed resistance exercise training while they were on the weight loss diet compared to when they consumed the same diet without training.
In addition to measuring the overall rate of muscle protein synthesis, in this study we used a novel technique to measure the rates of synthesis of individual proteins within skeletal muscle for the first time in older adults. We found that the performance of resistance training during the weight loss diet increased the synthesis of majority (175 of 190 measured) of individual skeletal muscle proteins, compared to the diet alone. Intestingly, these proteins included not only those that are involved in muscle contraction and muscle structure, but also proteins involved in energy production and other cell processes. These findings provide new and unique insight into the impact of resistance exercise training on skeletal muscle.
We found that there was little difference in the rate of muscle protein synthesis when comparing an even spread of protein over the daily meals and a traditional, skewed protein intake pattern during weight loss.
This suggests that while resistance exercise training has a very potent effect on muscle protein synthesis during weight loss the distribution of protein intake over the day has a much more subtle effect.
This study highlights that resistance exercise substantially raises rates of muscle protein synthesis during weight loss and may help older adults achieve the ultimate goal of preserving their muscle mass while reducing their fat mass.
Future research is needed to investigate dietary strategies that may further enhance the muscle mass-preserving effects of resistance exercise during weight loss on in obese older adults.
In this study 20 overweight and obese older men were provided with a reduced calorie diet for 4 weeks. The first two weeks of the study were the “diet only” phase during which the men maintained their normal physical activity levels and ate the reduced calorie diet. The second two weeks of the study were the “diet plus exercise” phase during which the men continued on the same calorie restricted diet but also performed supervised resistance exercise training three days per week.
To investigate the impact of protein intake pattern, ten of the men were given diets in which the protein was evenly spread over the daily meals (even group), while the other ten ate the protein in a traditional skewed pattern (skewed group) for the duration of the 4-week weight loss study.
The rate of muscle protein synthesis was measured over the 2-week “diet only” phase and over the 2-week “diet plus exercise” phase in the even group and the skewed group. To measure muscle protein synthesis we asked the men to drink “heavy water” throughout the 4 week study. Heavy water is very similar to normal drinking water but it contains a tracer that labels amino acids (the building blocks for new muscle protein) in the body. Then, during muscle protein synthesis these labeled amino acids are incorporated into newly built muscle tissue. We obtained muscle biopsies from the men at the start of the study, at the end of the the “diet only” phase and at the end of the “diet plus exercise” phase and measured how much of the heavy water label was incorporated into the muscle tissue. This allowed us to then calculate the rates of muscle protein synthesis.
Recent Publication
About the Author
Dr Caoileann Murphy is a postdoctoral research dietitian at the UCD Conway Institute of Biomolecular and Biomedical Research. After qualifying as a dietitian in 2009, Dr Murphy worked clinically at St. James's Hospital in Dublin before completing a Masters in Sport and Exercise Nutrition at Loughborough University in the UK.
Following this, she undertook a PhD at McMaster University, Canada, where she used stable isotopic tracers to examine the ability of practical nutrition and exercise strategies to maximize in vivo rates of muscle protein synthesis in older adults.
Dr Murphy has authored a number of scientific research papers, reviews and book chapters and is a recipient of the TOPMed10 Marie Curie Fellowship.
Earlier this month, Dr Murphy was named as the latest recipient of the British Nutrition Foundation’s Drummond Early Career Scientist Award and will be honoured at a ceremony in London later this month. The Drummond Early Career Scientist Award is an annual scheme run by the British Nutrition Foundation. It recognises early career nutrition scientists who show great potential to be future leaders in the field.
Along with receiving an award, Dr Murphy’s work will be showcased in December’s edition of Nutrition Bulletin.
